You should know:
-- I'm currently using GEF just as a visualization tool, for visualizing a model
-- the editing capabilities of GEF will be used later in the project
-- I've have to work with a model I'm not allowed to change
-- the model has no update/notification mechanism
-- no editing capabilities are required at the moment, except of moving the elements
of the diagram (if you like to call this editing)
-- no view information (positions, width, height, ...) is stored in the model, at all

At the moment I'm trying to add connections to my visualization.
Therefo some of the EditParts implement NodeEditPart and thus provide all information
for the connections. As far as I can see, the connections (its editparts) are created correctly.

Unfortunately, the connections are not shown in the editor.

I've read a lot about it and figured out that I have to call refreshSourceConnections(), and refreshTargetConnections().

But all the solutions I've found depend either on the notification of the view by the model, which I don't have.
Or depend on a creation command for connections, that I also don't have.

The bug in short:
Imagine a classdiagram (classes A,B) with possible associations:
A - B, A -> B, A <-> B, A <- B.

Now I added associations A - B, as imcoming and outgoing connections in A and B,
which is clearly not really what I want.
It apparently leads to only one connection: A - A, which is not shown or not really visible.